The first is the CHEN diagram. This describes the relationship between entities (1:M, M:N, 1:1). In this notation, the entities are noted in rectangular boxes. The relation is noted in a diamond shape between the two boxes representing entities. The three "shapes" are connected via straight lines:

The second notation that is more commonly seen by Oracle users (and used in Designer 2000 ERDs) is known as the Crow's Foot Model.

Like the Chen diagram, the entity is described in a box (usually in the singular, rather than plural). The relation is described by the different shapes of "Crow's Foot". E.g. it may be dashed or solid lines. And the lines may branch into three at the end indicating a X to many relationship.
__ __
| |_____/_ | |
|__| \ |__|

You may also have what's known as a sow's ear, which is a relation of one entity with itself (a recursive relationship).